There are implantable active medical devices, such as the well known double chamber devices, which collect (sense or detect) and deliver (stimulate) signals in the high (atrial) and low (ventricular) cavities of the heart. These apparatus are conceived in order to follow the cardiac rhythm of a patient and to perform one or more functions for the diagnosis and/or therapy of atrial (AA) and/or ventricular (AV) arrhythmias. These diagnostic and therapeutic functions, which are also known as control functions, are executed in response to the arrhythmias (AA or AV) that present a predefined pattern, with isolated extra-systoles, extra-systoles occurring in salvos, and the so-called troubles of rhythm (abnormally fast rhythms), but they could be operating improperly based on changes between these different patterns due to extra-systolic events. The consequence can be an inappropriate diagnosis, with a possibly of the application of a therapy that is inappropriate and perhaps harmful.
Generally, one defines two types of ventricular extra-systoles (ESV). A ventricular extra-systole of the first type corresponds to a detection or ventricular stimulation which is not preceded by an atrial event (i.e., a detection of a spontaneous beat or a stimulation pulse delivered by the device in the atrium) in a time interval considered as physiological, for example, between 31 and 300 ms. A ventricular extra-systole of the second type corresponds to a ventricular detection preceded by an atrial event in an interval of time between 31 and 300 ms, in the case where the atrio-ventricular delay (AR) of the examined cycle is more than 31 ms less than the atrio-ventricular delay period (DAV) of the preceding cardiac cycle (DAV-AR&gt;31 ms), a cardiac cycle being defined as the interval of time between two events of a similar nature in the same cavity. For further details on the processing of ventricular extra-systoles, reference is made EP A 550 342, and its corresponding U.S. Pat. No. 5,312,451 which is incorporated herein by reference, describing an algorithm of specific actions after the detection of a ventricular extra-systole.
A "P" wave or an "event P` (the collection of a spontaneous cardiac event having its origin in the atrium) is defined as an atrial extra-systole (ESA) if the interval of time separating this P wave from the preceding atrial event is less than a fraction of the average interval of the atrial frequency calculated over a number cardiac cycles, e.g., eight cycles, not comprising an extra systole (average PP).
Further, one finds defined in the literature a class of extra-systoles known as doublets (double) or triplets (triple), that are, respectively, a continuation of two extra-systoles (ESA or ESV) without an intermediary event not of extra-systolic origin or a continuation of three extra-systoles without an intermediary event not of extra-systolic origin. These extra-systole doublets or triplets occur according to a sequence of some repetition.
There also is known the so-called "salvo" of extra-systoles, which is a sequence of very close repetitions of extra-systoles (atrial or ventricular) presenting multiple events without any intermediary event not of an extra-systolic origin. These extra-systole salvos are cardiac events that are worrisome, and their presence is a sign of the seriousness or gravity of the cardiac prognosis of the patient. Salvos of extra-systoles can necessitate the delivery of a defibrillation shock, if they degenerate in the ventricle into a fibrillation.
One defines also a trouble of the sustained rhythm as salvoes whose duration is greater than a predetermined time (typically 30 s).